In laser cutting, a cutting gas flows around a laser beam, a workpiece is melted by energy of the laser beam radiated to the workpiece and oxidation reaction energy between the workpiece and the cutting gas, and a melted metal is discharged by the kinetic energy of the cutting gas.
When the workpiece is cut by such laser cutting, an end point of the laser cutting may be set such that a laser nozzle is separated from the workpiece in a preset shape. However, for example, when oxygen is used as the cutting gas such as when cutting a soft steel material, depending on the cut shape or material and a surface state, an excessively wide range on the workpiece may reach a high temperature, and the workpiece may be excessively melted such that a desired shape in the vicinity of a cutting end point cannot be secured.
Here, in order to secure the desired shape in the vicinity of the end point of the laser cutting, for example, in general, the cutting is performed while a micro joint remains as shown in FIG. 5A. Otherwise, in general, a cutting relief as shown in FIGS. 5B to 5D is performed. Here, solid lines in FIGS. 5A to 5D show edge sections of kerfs, hatched circles show piercing holes, and broken lines and arrows on the broken lines show trajectories of the laser nozzle.
However, when the cutting is performed while the micro joint remains, the micro joint should be separately cut, and the number of cutting processes and the total cutting costs are increased. In this respect, for example, a technique of forming a small micro joint and improving machining efficiency is disclosed (for example, see Patent Literature 1).
Meanwhile, in the cutting relief, scratching is likely to occur in the vicinity of the end point of the cutting.